Method and system for transmitting data, with transmission antenna diversity

ABSTRACT

The present invention creates a data transfer method, specifically for use in a CDMA system in the TDD mode, a data signal being transmitted in the form of a data stream of data bursts of different users (N 1 -NK) between a first station (BS) and a second station (MS) via a multiplicity of antennas (A 1 -AN), and a reference signal being transmitted in connection with the specific data burst. In a first step, a reference signal is transmitted from the second station (MS) to the first station (BS). In a second step, a channel estimation (KS) is carried out in the first station (BS) based on the reference signal that is received from the second station (MS). In a third step, the first station (BS) transmits a data burst to the second station (MS) via the multiplicity of antennas (A 1 -AN), it being possible to modify the transmission signals of various antennas having various amplitude and phase factors (A n , φ n ) in accordance with the channel estimation.

BACKGROUND INFORMATION

[0001] The present invention relates to a data transfer method and system, especially for use in a CDMA system in the TDD mode, a data signal being transmitted in the form of a data stream of data bursts of different users between a first station and a second station via a multiplicity of antennas, and a reference signal being transmitted in connection with each specific data burst.

[0002] Although it can in principle be applied to any data transmissions, the present invention and the problem underlying it are discussed with respect to a cellular CDMA data-transmission system (CDMA=Code Division Multiple Access), which employs a transmission mode that requires the transmission of a reference signal.

[0003] Using code multiple access (CDMA=Code Division Multiple Access), it is possible to transmit a multiplicity of data streams at the same time over one common frequency band. In this context, the symbols of the data streams to be transmitted are modulated using so-called spreading codes.

[0004] The data streams transmitted simultaneously using different codes usually interfere with each other: multi-path diffusion leads to the superimposition of sequentially transmitted data symbols (inter-symbol interference, ISI). CDMA coding and multi-path diffusion are the cause of multiple-user interference (multiple access interference, MAI).

[0005] The interferences can be eliminated, e.g., in the receiver, if the impulse response of the channel there is known, as can be seen from K. D. Kammeyer: “Message Transmission,” 2nd edition, Information Technology Series, Teubner, Stuttgart, 1996, and from A. Klein, G. K. Kaleh, and P. W. Baier, “Zero Forcing and Minimum Mean-Square-Error Equalization for Multiuser Detection in Code Division Multiple Access Channels,” IEEE Trans. Vehic. Tech., Vol. 45 (1996), 276-287. The channel impulse response can be estimated from a received reference signal, e.g., in the receiver.

[0006] To assure a constantly satisfactory transmission, it is also possible to transmit data simultaneously over a plurality of mobile radio channels. This can be achieved using a plurality of transmitting antennas (transmitting antenna diversity). Transmitting antenna diversity of this kind improves the quality of mobile-radio-channel transmissions in a remarkable manner.

[0007] For CDMA mobile radio systems in the TDD mode, the following transmitting antenna diversity schemes are known for the forward link (downlink), thus, e.g., from a base station to a mobile station.

[0008] In the Transmit Adaptive Array (TxAA) according to Motorola: “Transmit Diversity Schemes applied to the TDD mode (II),” 3GPP TSG RAN WG1 document TSGR1#5(99)632, the signals of the individual users, before their summation in the baseband, are modified using a phase and amplitude factor

[0009] In the Selection Transmit Diversity (STD) according to Motorola: “Transmit Diversity Schemes applied to the TDD mode (II),” 3GPP TSG RAN WG1 document TSGR1#5(99)632, the signals of the individual users are always emitted over only one antenna. For different users, different antennas can be selected.

[0010] In the Phase Alignment Transmit Diversity (PATD) according to Motorola: “Transmit Diversity Schemes applied to the TDD mode,” 3GPP TSG RAN WG1 document TSGR1#3(99)186, the overall antenna signals are modified in the baseband using a phase factor. The factor can be different for different antennas. It is identical for all users on one antenna.

[0011] In all of these schemes, the transmission qualities of the mobile radio channels in the counter link are determined in the transmitter. On the basis of the measured qualities, the parameters of the schemes are then selected (Closed Loop Technology).

[0012] To be able to detect data transmitted using TXAA or STD in accordance with a Joint Detection Method (JD), it is necessary for every user to carry out its own channel estimation in the receiver.

[0013] When PATD is used, it is only necessary in the forward link to estimate one channel in the JD receiver. However, in contrast to TXAA and STD, PATD has the disadvantage of not employing any amplitude modifications for optimizing the transmission.

[0014] Customary diversity methods for the CDMA transmission in the forward link in the TDD mode therefore either require great expense for channel estimation in the receiver (TxAA=Transmit Adaptive Array, STD=Selection Transmit Diversity), or they should be further improved qualitatively (PATD=Phase Alignment Transmit Diversity).

ADVANTAGES OF THE INVENTION

[0015] The idea underlying the present invention is that the transmission signals of the individual antennas are modified both in their phase as well as in their amplitude.

[0016] The method according to the present invention having the features of claim 1, and the corresponding device according to claim 6, have the particular advantage that it is possible to achieve an improvement of the data transmission by transmitting via a multiplicity of antennas without the necessity of a plurality of channel estimations in the forward link in the JD reception. When the method is used in the forward link, it is only necessary to carry out one channel estimation in the JD receiver. In particular, an improved transmission is possible compared to the use of PATD.

[0017] In the subclaims can be found advantageous refinements and improvements of the specific subject matter of the present invention.

[0018] According to one preferred refinement, the phase and amplitude factors are kept constant during successive time segments.

[0019] According to one further preferred refinement, phase factors φ_(n) and amplitude factors A_(n) are selected so that a maximization of the product ${P\left( {\phi_{1},\ldots \quad,\phi_{N},A_{1},\ldots \quad,A_{N}} \right)} = {\prod\limits_{k = 1}^{K}\quad {{\sum\limits_{n = 1}^{N}{\alpha_{n}^{k} \cdot A_{n} \cdot _{n}^{i\quad \phi}}}}^{2}}$

[0020] is achieved by varying antenna-specific phases φ_(n) and amplitudes A_(n), given the secondary conditions ${\phi_{1} = {{0\quad {and}\quad {\sum\limits_{n = 1}^{N}A_{n}^{2}}} = {{const}.}}},$

[0021] the channel estimation coefficient of the greatest output of the channel from the nth antenna to the kth user being designated as α_(n) ^(k), it being true that: n=1, . . . , N and k=1, K where N=number of antennas and K=number of users.

[0022] According to a further preferred refinement, the first station is a base station, and the second station is a mobile station of a mobile radio system in the TDD mode, in particular a UMTS mobile radio system.

[0023] According to a further preferred refinement, the transmission is carried out using the CDMA method.

DRAWINGS

[0024] An exemplary embodiment of the present invention is depicted in the drawing and is discussed in greater detail in the following description.

[0025] The following are the contents:

[0026]FIG. 1 depicts a schematic representation of one embodiment of the device according to the present invention for transmitting data over a multiplicity of antennas; and

[0027]FIG. 2 depicts a schematic representation of the temporal sequence of one embodiment of the method according to the present invention for transmitting data over a multiplicity of antennas using the device depicted in FIG. 1.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0028] In the Figures, the same reference numerals designate the same or functionally equivalent elements.

[0029] In FIGS. 1 and 2, N1 through NK designate specific users of the device, 101 through 10K a specific adder, 201 through 20K a specific multiplier, A1 through AN and AM a specific antenna, BS a base station, MS a mobile station, S a transmission step, KS a channel estimation step, SDIV a transmission step having antenna diversity, and E a reception step.

[0030] The specific embodiment is a UMTS (Universal Mobile Telephone System) system in the TDD mode, the data signal being transmitted in the form of a data stream of data bursts of various users between a base station BS and a mobile station MS via a multiplicity of antennas A1-AN, and a reference signal being transmitted in connection with the respective data burst.

[0031] In this context, the transmission having transmission antenna diversity is realized in the following way.

[0032] First, an estimation takes place, in the usual manner, of the channels of all users N1 through NK in the reverse link via base station BS on the basis of a reference signal that is transmitted from the mobile station.

[0033] Thereafter, the determination of the highest output of the channel path is carried out for every user channel. The associated channel estimation coefficient of the channel from the nth antenna to the kth user is designated as α_(n) ^(k), it being true that: n=1, . . . , N and k=1, . . . , K where N=the number of antennas and K=number of users (in each case natural numbers).

[0034] Then a maximization of the product ${P\left( {\phi_{1},\ldots \quad,\phi_{N},A_{1},\ldots \quad,A_{N}} \right)} = {\prod\limits_{k = 1}^{K}\quad {{\sum\limits_{n = 1}^{N}{\alpha_{n}^{k} \cdot A_{n} \cdot _{n}^{i\quad \phi}}}}^{2}}$

[0035] is carried out by varying antenna-specific phases φ_(n) and amplitudes A_(n) given the secondary conditions $\phi_{1} = {{0\quad {and}\quad {\sum\limits_{n = 1}^{N}A_{n}^{2}}} = {{const}.}}$

[0036] Then, the transmission takes place of entire CDMA signal A_(n)·e^(iφ) _(n)·s (t) modified by phase φ_(n) and amplitude A_(n), where s(t)=overall CDMA signal, via the nth transmission antenna of the forward link, as depicted in FIG. 1, to the mobile station.

[0037]FIG. 2 depicts the temporal sequence of the data transfer method. In contrast to PATD, this method varies not only antenna-specific phases φ_(n) but also amplitudes A_(n).

[0038] Initially, mobile station MS transmits a data burst having a reference signal data block to base station BS, which uses the data block for channel estimation. Based on the result of the channel estimation, the base station carries out channel estimation KS. Then the aforementioned transmission of data having antenna diversity SDIV is carried out from the base station to the mobile station, followed by reception E there.

[0039] Although the present invention was described above on the basis of a preferred exemplary embodiment, it is not limited thereto, but rather can be modified in many ways.

[0040] In particular, the method according to the present invention can be used in all data-transmission systems and is not limited to CDMA data transmission systems in the TDD mode.

[0041] In addition, the detection method for the amplitudes and phases can also be varied. 

What is claimed is:
 1. A data transfer method, specifically for use in a CDMA system in the TDD mode, a data signal being transmitted in the form of a data stream of data bursts of different users (N1-NK) between a first station (BS) and a second station (MS) via a multiplicity of antennas (A1-AN), and a reference signal being transmitted in connection with the specific data burst; furthermore, i) in a first step, a reference signal being transmitted from the second station (MS) to the first station (BS); ii) in a second step, a channel estimation (KS) being carried out in the first station (BS) based on the reference signal received from the second station (MS); and iii) in a third step, the first station (BS) transmitting a data burst to the second station (MS) via the multiplicity of antennas (A1-AN), it being possible to modify the transmission signals of various antennas using various amplitude and phase factors (A_(n), φ_(n)) corresponding to the channel estimation.
 2. The method as recited in claim 1, wherein the phase and amplitude factors are kept constant during successive time segments.
 3. The method as recited in claim 1 or 2, wherein phase factors φ_(n) and amplitude factors A_(n) are selected so that a maximization of the product ${P\left( {\phi_{1},\ldots \quad,\phi_{N},A_{1},\ldots \quad,A_{N}} \right)} = {\prod\limits_{k = 1}^{K}\quad {{\sum\limits_{n = 1}^{N}{\alpha_{n}^{k} \cdot A_{n} \cdot _{n}^{i\quad \phi}}}}^{2}}$

is achieved by varying the antenna-specific phases φ_(n) and amplitudes A_(n), given the secondary conditions ${\phi_{1} = {{0\quad {and}\quad {\sum\limits_{n = 1}^{N}A_{n}^{2}}} = {{const}.}}},$

the channel estimation coefficient of the greatest output of the channel from the nth antenna to the kth user being designated as α_(n) ^(k), and it being true that: n=1 . . . , N and k 1, . . . , K where N=number of antennas and K=number of users.
 4. The method as recited in claim 1, 2, or 3, wherein the first station (BS) is a base station, and the second station (MS) is a mobile station of a mobile radio system in the TDD mode, in particular, a UMTS mobile radio system.
 5. The method as recited in one of claims 1 through 4, wherein the transmission is carried out using the CDMA method.
 6. A data transmission device, specifically for use in a CDMA system in the TDD mode, it being possible to transmit a data signal in the form of a data stream of data bursts of different users (N1-NK) between a first station (BS) and a second station (MS) via a multiplicity of antennas (A1-AN), and to transmit a reference signal in connection with the specific data burst; the first station (BS) also having: a receiving device for receiving a reference signal that is transmitted from the second station (MS) to the first station (BS); a channel estimation device for carrying out a channel estimation (KS) based on the reference signal received from the second station (MS); and a modification device for modifying the transmission signals of various antennas using various amplitude and phase factors (A_(n), φ_(n)) corresponding to the channel estimation for a data burst to be transmitted to the second station (MS) via the multiplicity of antennas (Al-AN).
 7. The device as recited in claim 6, wherein the modification device holds constant the phase and amplitude factors during successive time segments.
 8. The device as recited in claim 6 or 7, wherein the modification device selects the phase factors φ_(n) and amplitude factors A_(n) such that a maximization of the product ${P\left( {\phi_{1},\ldots \quad,\phi_{N},A_{1},\ldots \quad,A_{N}} \right)} = {\prod\limits_{k = 1}^{K}\quad {{\sum\limits_{n = 1}^{N}{\alpha_{n}^{k} \cdot A_{n} \cdot _{n}^{i\quad \phi}}}}^{2}}$

is achieved by varying the antenna-specific phases φ_(n) and amplitudes A_(n), given the secondary conditions ${\phi_{1} = {{0\quad {and}\quad {\sum\limits_{n = 1}^{N}A_{n}^{2}}} = {{const}.}}},$

the channel estimation coefficient of the maximum output of the channel from the nth antenna to the kth user being designated as α_(n) ^(k), and it being true that: n=1, . . . , N and k=1, . . . , K where N=number of antennas and K=number of users.
 9. The device as recited in claim 6, 7, or 8, wherein the first station (BS) is a base station, and the second station (MS) is a mobile station of a mobile radio system in the TDD mode, in particular, a UMTS mobile radio system.
 10. The device as recited in one of claims 6 through 9, wherein the transmission can be carried out using the CDMA method. 